1. Technical Field
The present invention relates in general to a disk drive unit and, in particular, to system and method for constraining vibration in a hard disk drive.
2. Description of the Related Art
A hard disk drive (hereinafter, a HDD), which is most commonly used as data storage means for computers, comprises a single or multiple magnetic disks on the same shaft, which is rotated by a spindle motor. Reading and writing of data is performed by a magnetic head placed facing the magnetic disk, wherein the magnetic head is driven by an actuator, which is commonly a voice coil motor (hereinafter, a VCM). The magnetic disk, magnetic head and actuator are accommodated in a chassis called disk enclosure. The disk enclosure is composed of a thin box-shaped aluminum alloy base and a top cover for sealing an opening of the base.
Major technical problems for HDDs include increasing the storage capacity per magnetic disk and increasing the speed of reading data from and writing to the magnetic disk, etc. Concerning the latter, the speed for reading and writing data can be improved by reducing the seek time necessary for the magnetic head to move to a desired track on the magnetic disk. Since the magnetic head is driven by the VCM as described above, the seek speed can be increased by improving the performance of the VCM. In order to improve the performance of the VCM, it may be necessary to increase the magnetic property of the permanent magnet of the VCM or to increase the thickness of the magnet to increase the magnetic field applied to the voice coil. However, the magnetic property of the permanent magnet has been approaching its limit. Besides, it is difficult to increase the thickness of the permanent magnet than at present since the space-saving is strongly required for HDDs. Alternatively, the speed for reading and writing data can be increased by increasing the speed of rotation of the magnetic disk. However, this may cause the problem of acoustic noise or vibrations.
In the prior art, various countermeasures have been made to overcome acoustic noise and vibrations. For example, Japanese Published Unexamined Patent Application (PUPA) No. 2001-43658 discloses a structure where an adherent visco-elastic material is inserted into a gap between a fixed shaft of the spindle motor and a top cover or a gap between an upper yoke of the VCM and the top cover, etc. Also, PUPA No. 1996-167259 and PUPA No. 1997-213029 disclose structures where an adherent visco-elastic material is inserted between an upper yoke of the VCM and a top cover.
3. Problems to be Solved by the Invention
The prior art references described above show that the VCM has a significant influence on acoustic noise or vibrations in HDDs. Unfortunately, in spite of the countermeasures described above, the acoustic noise or vibrations are remarkable at the seek time of the magnetic head. Therefore, it is an object of the present invention to further decrease acoustic noise or vibrations of HDDs.